Electrophilic terminal-phosphinidene complexes: Versatile phosphorus analogues of singlet carbenes

Electrophilic and nucleophilic terminal-phosphinidene complexes are compare d in terms of electronic structures and reactivities. Various precursors of the unstable electrophilic species [R=P=M] (M=Cr, Mo, W(CO)(5) and Fe(CO)( 4)) are discussed. The addition reactions of the electrophilie phosphiniden e complexes with Lewis bases, insertion reactions into O-H, N-H, and activa ted C-H bonds and cycloaddition reaction, with double and triple bonds are described, as well as some rearrangements and auto-condensations. Various a pplications to the synthesis of new organophosphorus molecules are discusse d and techniques available for demetallation are given.